This invention relates to magnetic sensors, and more particularly, to magnetic sensors capable of detecting the presence, magnitude, and direction of an external magnetic field and useful as azimuth, position, inclination, electric current and other sensors.
Magnetic sensors are used to detect the presence or absence, magnitude, and direction of an external magnetic field. Most magnetic sensors are of the design that a magnetic core has an exciting winding and a pick-up winding wound thereon. Referring to FIG. 19, there is illustrated a prior art conventional magnetic sensor comprising a magnetic core 1 and exciting and detecting windings 2 and 3 wound thereon. In the illustrated arrangement, the core 1 typically in the form of a rod is placed such that its axis is in alignment with the direction of an external magnetic field H0. Alternating current is supplied through the exciting winding 2 from a power supply 4 to produce an internal magnetic field Hi in the magnetic core 1 in an axial direction thereof. In response to the thus produced internal magnetic field Hi, an output voltage in the form of a wave fundamental or harmonic to the input appears at an output terminal 5 of the detecting winding 3. Since the external magnetic field H0 acts to bias the internal magnetic field Hi, the output voltage varies with the magnitude of the external magnetic field H0. In this way, the illustrated arrangement detects the magnitude of the external magnetic field H0. This type of magnetic sensor may be used as an electric current sensor, for example, in which a variation in magnitude of an external magnetic field H0 which varies with the magnitude of an electric current is detected as a variation of output voltage.
FIG. 20 illustrates another application of the magnetic sensor of FIG. 19. The magnetic sensor and means for producing an external magnetic field are placed such that the relative position (depicted by an angle .theta.) of the magnetic core 1 and the external magnetic field H0 are variable. In response to the internal magnetic field Hi induced in the magnetic core 1, a variation of a component of the external magnetic field H0 in the axial direction of the core 1, H0. cos .theta., appears as a variation of the output voltage. These magnetic sensors can be used alone or as a combination of two or more as an azimuth or inclination sensor.
The principle of operation of the magnetic sensors shown in FIGS. 19 and 20 is briefly described with reference to FIG. 21. In either case, the direction of a magnetic flux of an external magnetic field H0 or a component thereof is in parallel with the direction of an internal magnetic field Hi as shown in FIG. 21A. The strength of the resultant magnetic field reaches maximum when the external and internal magnetic fields H0 and Hi have the same direction as shown in FIG. 21B, but minimum when the external and internal magnetic fields H0 and Hi have opposite directions as shown in FIG. 21C. Such a variation is detected as a variation of output voltage.
The magnetic sensors shown in FIGS. 19 and 20 require two windings, exciting and detecting windings 2 and 3, resulting in a rather complicated structure.
Another prior art well-known magnetic sensor is a sensor based on a Hall element, which suffers from poor sensitivity.